release/1.6.0: bugfix for mapl with mvapich2, and bug fix for grib-utils modulefile (wgrib env var)

[climbfuji]

Summary

For release/1.6.0:

• bugfix for mapl with mvapich2 (see release/1.60: bug fix for mapl with mvapich2 spack#449)
• bugfix for grib-utils module file (wgrib env var) - I don't know why this was never committed to the release branch, instead changes were made locally only :-(

Corresponding upstream spack develop PR for mapl/mvapich2: spack/spack#45164

Testing

Installed successfully on Hercules with gcc and mvapich2

Applications affected

n/a

Systems affected

n/a

Dependencies

• waiting for release/1.60: bug fix for mapl with mvapich2 spack#449

Issue(s) addressed

Required for #1168

Checklist

• This PR addresses one issue/problem/enhancement, or has a very good reason for not doing so.
• These changes have been tested on the affected systems and applications.
• All dependency PRs/issues have been resolved and this PR can be merged.